In the past 10 years, liquid crystals have been introduced into various technical fields (for example, watch, electric calculator and typewriter displays) wherein the electrooptical properties and the characteristics of liquid crystals in a display device are required. These liquid crystal devices are based on the dielectric alignment effects of liquid crystal compounds in nematic, cholesteric or smectic phases. In such a liquid crystal phase, the long axis of a molecule of the compound is selectively aligned under the electric field applied thereon due to its dielectric anisotropy. The usual response time of a display device is too long to use in a number of other fields where liquid crystals can be applied. This problem is particularly serious when it is necessary to apply an electric field to a number of pixels. To solve this problem, it is effective to employ an active mode with the use of a thin film transistor (TFT). However, it generally costs too much to produce an instrument having a relatively large screen size.
In addition to nematic and cholesteric liquid crystals, the importance of optically active smectic liquid crystal phases has greatly increased in these several years.
Clark and Lagerwall demonstrated that an electrooptical switching or display device, which shows a response speed 1,000 times higher than that of a conventional twisted nematic (TN) cell, can be obtained by employing a ferroelectric liquid crystal system in an extremely thin cell see, for example, Lagerwall et al., "Ferroelectric Liquid Crystal Displays", SID Symposium, October Meeting, 1985, San Diego, Calif., USA, hereby incorporated by reference!. Because of having these characteristics as well as other favorable properties including bistable switching, wide viewing angle characteristics and high contrast, ferroelectric liquid crystals (FLC) are principally suitable for the above-mentioned fields, for example, those wherein matrix addressing are employed.
Known methods for aligning ferroelectric liquid crystals include the rubbing method and the oblique vapor-deposition method. In the rubbing method, an organic polymer film is formed on a transparent electrode by spin coating or printing, and then the organic polymer film is rubbed by rotating a roller having an organic polymer cloth wound around the same to align liquid crystal molecules in the rubbing direction. Although this method is highly suitable for mass production, a panel obtained by this method has only a small pretilt angle (i.e., a liquid crystal alignment inclination angle to a substrate) of 0.degree. to 10.degree..
When a larger pretilt angle is needed, the oblique vapor-deposition method is employed with the use of an inorganic substance such as SiO. By using this method, it is possible to overcome the problem of zigzag defects and to obtain a monodomain alignment having a large pretilt angle.
To obtain an alignment free from any defects, it is generally required to fill a liquid crystal into a cell prepared by one of the above-mentioned aligning methods or another method, and then gradually cool the cell as described in JP-B-6-64273, hereby incorporated by reference.
However, it is sometimes impossible to obtain a completely defect-free alignment by the above-mentioned method involving gradual cooling. Particularly when a rough interface is formed by the oblique vapor-deposition method or spacers are scattered on the surface, the unevenness on the surface of the alignment layer provides nuclei and thus disclination lines are formed in the nematic phase, or in some cases, twisted alignments exist. These defects in the nematic phase remain as such even in the smectic phase, thus deteriorating the display performance.